Since estrogen deficiency in women has been reported to lead to impairments in cognitive function, it is important to determine whether long-term ovariectomy exacerbates the cognitive decline that occurs in normal aging. We have investigated this possibility in aged rhesus monkeys. We compared the performance of aged female monkeys that were ovariectomized early in life to age-matched controls with intact ovaries using tasks of object memory, spatial memory, and executive functions. The ovariectomized female monkeys were impaired on a Delayed Non-Matching-to-Sample task with a 600-second interval, but were better than controls on a spatial memory task, the spatial condition of the Delayed Recognition Span Test. These findings suggest that prolonged deprivation of circulating estrogens in females exacerbates the decline in object memory that accompanies normal aging but protects against the development of spatial memory deficits with age. In a complementary stud y to exam ine sex differences in aging, we found that young males and females performed similarly on tasks of object memory and executive function, but young males outperformed young females on a spatial memory task (Delayed Recognition Span Test) that requires the identification of a new stimulus among an increasing array of serially-presented stimuli. This superior level of spatial ability in young males declined sharply with age, so that old males did not perform significantly better than old females. These findings in the nonhuman primate suggest that biological rather than sociocultural factors underlie the sex differences in cognition and their diminution with age. FUNDING NIH / AG00001 $133,837 2/01/97 - 1/31/00 PUBLICATIONS Herndon, J.G., Constantinidis, I. and Moss, M.B. Age-related brain changes in rhesus monkeys a magnetic resonance spectroscopic study. NeuroReport 9:2127-2130, 1998. Herndon, J.G., Tigges, J., Klumpp,S.A. and Anderson, D.C. Brain weight does not decrease with age in adult rhesus monkeys. Neurobiol. Aging 19:267-272, 1998. Lacreuse, A., Herndon, J.G. and Moss, M.B. Vieillissement des fonctions cognitives chez l'homme et le macaque rhsus (Macaca mulatta). Primatologie 1:333-377, 1998. Moss, M.B., Killiany, R.J. and Herndon, J.G. Neurobiological basis of cognitive decline in the aged monkey. In Cerebral Cortex A. Peters and J. Morrison (Eds.) (In press). P51RR00165-38 1/1/98 - 12/31/98 Yerkes Regional Primate Research Center